Lipid biomarkers of deep-sea hydrothermal vent polychaetes—Alvinella pompejana, A. caudata, Paralvinella grasslei and Hesiolyra bergii

The lipid composition was determined for 5 species of polychaete annelids collected by the Deep Submergence Vehicle ALVIN from high temperature chimneys at the 2500 m depth hydrothermal vent field of the East Pacific Rise. These are the first lipid biomarker analyses reported for these hydrothermal vent polychaetes. Lipid content was low in all samples (1.6–35.9 mg g^–1 wet mass) and was dominated by polar lipid (78–90% of total lipid) with 8–19% sterol (ST), and very low storage lipid (triacylglycerol and wax ester). Total polyunsaturated fatty acids (PUFA) were moderately high (22–31% of total fatty acids (FA)) with extremely low or no docosahexaenoic acid (DHA, 22:6(n-3)). Eicosapentaenoic acid (EPA, 20:5(n-3)) levels were 5–6% in Alvinella pompejana and A. caudata and 10.3–13.7% in an errantiate polychaete (likely Hesionidae) and Hesiolyra bergii. There were greater PUFA and a greater EPA/AA (AA is arachidonic acid, 20:4(n-6)) ratio in the anterior versus the posterior half of A. pompejana, which may correlate to the strong temperature gradient reported in its tube. Total nonmethylene interrupted diunsaturated fatty acids (NMID) were 4–9% of total FA for most polychaete species and included several 20:2 and 22:2 components. The principal monounsaturated fatty acids (MUFA) included 18:1(n-7)c (14–19%), 16:1(n-7)c (2.6–10%) and 20:1(n-11)c (3–7% of total FA). These polychaete species may desaturate and elongate the bacterial-derived 18:1(n-7)c to obtain the essential FA EPA and AA. The major ST in the polychaetes is cholesterol (89–98% of total ST) with less cholesterol in the gut contents of A. pompejana. Other ST included 24-ethylcholesterol (1.5–5% of total ST) with lesser amounts of 24-methylenecholesterol, desmosterol, lathosterol, 24-methylcholesterol, 24-ethylcholesterol, and the stanols dehydrocholestanol and cholestanol. The high ST levels could play a role in thermal adaptation of membranes at the hydrothermal vent environment. Differences in the FA profiles separated the closely related species A. pompejana and A. caudata from Paralvinella grasslei, H. bergii, and the errantiate polychaete (likely Hesionidae).     

Structural analysis of the collar of the Vredefort Dome,South Africa—Significance for impact‐related deformation and central uplift formation

Abstract— Landsat TM, aerial photograph image analysis, and field mapping of Witwatersrand supergroup meta‐sedimentary strata in the collar of the Vredefort Dome reveals a highly heterogeneous internal structure involving folds, faults, fractures, and melt breccias that are interpreted as the product of shock deformation and central uplift formation during the 2.02 Ga Vredefort impact event. Broadly radially oriented symmetric and asymmetric folds with wavelengths ranging from tens of meters to kilometers and conjugate radial to oblique faults with strike‐slip displacements of, typically, tens to hundreds of meters accommodated tangential shortening of the collar of the dome that decreased from ?17% at a radius from the dome center of 21 km to <5% at a radius of 29 km. Ubiquitous shear fractures containing pseudotachylitic breccia, particularly in the metapelitic units, display local slip senses consistent with either tangential shortening or tangential extension; however, it is uncertain whether they formed at the same time as the larger faults or earlier, during the shock pulse. In addition to shatter cones, quartzite units show two fracture types—a cmspaced rhomboidal to orthogonal type that may be the product of shock‐induced deformation and later joints accomplishing tangential and radial extension. The occurrence of pseudotachylitic breccia within some of these later joints, and the presence of radial and tangential dikes of impact melt rock, confirm the impact timing of these features and are suggestive of late‐stage collapse of the central uplift.     

Geochemical and petrographic characteristics of impactites and Cretaceous target rocks from the Yaxcopoil‐1 borehole,Chicxulub impact structure,Mexico: Implications for target composition

Abstract— We present major and trace element data as well as petrographic observations for impactites (suevitic groundmass, bulk suevite, and melt rock particles) and target lithologies, including Cretaceous anhydrite, dolomite, argillaceous limestone, and oil shale, from the Yaxcopoil‐1 borehole, Chixculub impact structure. The suevitic groundmass and bulk suevite have similar compositions, largely representing mixtures of carbonate and silicate components. The latter are dominated by melt rock particles. Trace element data indicate that dolomitic rocks represented a significant target component that became incorporated into the suevites; in contrast, major elements indicate a strong calcitic component in the impactites. The siliceous end‐member requires a mafic component in order to explain the low SiO₂ content. Multicomponent mixing of various target rocks, the high alteration state, and dilution by carbonate complicate the determination of primary melt particle compositions. However, two overlapping compositional groups can be discerned—a high‐Ba, low‐Ta group and a high‐Fe, high‐Zn, and high‐Hf group. Cretaceous dolomitic rocks, argillaceous limestone, and shale are typically enriched in U, As, Br, and Sb, whereas anhydrite contains high Sr contents. The oil shale samples have abundances that are similar to the North American Shale Composite (NASC), but with a comparatively high U content. Clastic sedimentary rocks are characterized by relatively high Th, Hf, Zr, As, and Sb abundances. Petrographic observations indicate that the Cretaceous rocks in the Yaxcopoil‐1 drill core likely register a multistage deformation history that spans the period from pre‐ to post‐impact. Contrary to previous studies that claimed evidence for the presence of impact melt breccia injection veins, we have found no evidence in our samples from a depth of 1347–1348 m for the presence of melt breccia. We favor that clastic veinlets occur in a sheared and altered zone that underwent intense diagenetic overprint prior to the impact event.     

Visual observations of Comet Kohoutek from Skylab III

Visual observations of Comet Kohoutek (1973f) by the Skylab III astronauts are presented. They include the sighting of a sunward spike or “anti-tail” on the day after perihelion.     

The origin of the light distribution in spiral galaxies

We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatiotemporal evolution of both the disc age and metallicity distributions. We find a 'break' in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ∼60 per cent of the resident stars migrated from the inner disc, while ∼25 per cent formed in situ . Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an 'inside-out' formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction.     

The CQU Regional Seismic Network and applications to underground mining in Central Queensland,Australia

Digital seismograms continuously recorded from 1988 to 1992 by two stations of the RESNOM seismic network in northern Baja California, Mexico, were used to search for probable shear-wave anisotropic characteristics in the region of the Cerro Prieto fault. Shear-wave splitting was identified in many of the three-component records analyzed. We measured the polarization direction of the leadingS wave inside theS-wave window as well as the delay times between fast and slow phases on those records displaying shear-wave splitting. For station CPX, which is nearest the Imperial Valley region to the north, the preferred polarization direction found in this study (azimuth 180°±10°) coincides with the direction of the regional maximum compressive stress determined for the region. This polarization direction can be interpreted in terms of the “Extensive Dilatancy Anisotropy” model as the effect of vertical parallel aligned cracks. The preferred polarization direction measured at LMX, however, gives an azimuth of 45°±5°. Thus, it appears that faults and fractures aligned oblique to the main tectonic trend have a greater influence on the anisotropic characteristics of the crust south of Cerro Prieto volcano than that of the regional stress field. Time delays between slow and fastS waves observed at CPX appear constant from 1988 to 1992 while delays measured at LMX for the same interval indicate a small increase with time which cannot be attributed to azimuthal variations of paths.     

Retrogressive hydration of calc-silicate xenoliths in the eastern Bushveld complex: evidence for late magmatic fluid movement

Two calc-silicate xenoliths in the Upper Zone of the Bushveld complex contain mineral assemblages which permit delineation of the metamorphic path followed after incorporation of the xenoliths into the magma. Peak metamorphism in these xenoliths occurred at T=1100–1200°C and P <1.5 kbar. Retrograde metamorphism, probably coinciding with the late magmatic stage, is characterized by the breakdown of akermanite to monticellite and wollastonite at 700°C and the growth of vesuvianite from melilite. The latter implies that water-rich fluids (X_CO2 <0.2) were present and probably circulating through the cooling magmatic pile. In contrast, calc-silicate xenoliths within the lower zones of the Bushveld complex, namely in the Marginal and Critical Zones, also contain melilite, monticellite and additional periclase with only rare development of vesuvianite. This suggests that the Upper Zone cumulate pile was much ‘wetter’ in the late-magmatic stage than the earlier-formed Critical and Marginal Zone cumulate piles.     

The nature of the sea surface as deduced from composite temperature analysis

Summary A technique is described for preparing detailed sea surface temperature analyses for large ocean areas utilizing injection temperature observations from commercial ships. The inadequacies of analyses based on averaged data are discussed, as well as some of the difficulties inherent in contouring scalar fields.Sea surface temperatures are interpreted according to some concepts derived from cross sectional profiles and surface current data. Isotach analyses of mean current drift are considered as flow patterns to aid temperature analysis in areas where data are sparse.

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Die Schwankungen der Oberflächentemperatur des Meeres nach der zusammengesetzten Temperaturanalyse

Zusammenfassung Es wird eine Methode beschrieben, die geeignet ist, mittels Temperaturbeobachtungen von Handelsschiffen aus die Vorarbeiten zu detaillierten Analysen von Oberflächentemperaturen in großräumigen Meeresgebieten durchzuführen. Die Unzulänglichkeit von Analysen gemittelter Werte sowie einige Schwierigkeiten bei der graphischen Darstellung von Skalarfeldern werden besprochen.Gemäß den Vorstellungen, die von Querschnittsprofilen und Oberflächenstromwerten abgeleitet wurden, werden Oberflächentemperaturen gedeutet. Um die Temperaturanalyse in Gebieten mit geringen Beobachtungen zu erleichtern, werden Isotachen-Analysen mittlerer Strömungswerte als Strömungsvorbilder benutzt.

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La nature de la température superficielle de la mer suivant l'analyse composée de la température

Résumé L'article actuel décrit une méthode propre à préparer, au moyen des observations de la température faites au bord des navires marchands, des analyses détaillées de la température superficielle dans de grandes étendues océaniques. L'impropriété de l'analyse des valeurs moyennes ainsi que plusieurs difficultés que l'on rencontre en représentant des champs scalaires sont exposées.Suivant les conceptions déduites des coupes transversales et des courants de surface, on interprète les températures superficielles des courants de l'océan. Dans le but de faciliter l'analyse des températures dans de grandes zones océaniques où des observations sont rares, on se serve comme modèle de courant des analyses des isotaches des valeurs moyennes de courants.

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Submitted October 1961 for publication in Deutsche Hydrographische Zeitschrift.     

Dyke magnetization, magnetostratigraphy and upper-crustal structure in the Reydarfjordur area of eastern Iceland

A dyke swarm approximately 12 m.y. old and comprising 103 basaltic dykes was sampled during a palaeomagnetic investigation of the Reydarfjördur area, eastern Iceland. Of 100 dykes yielding statistically significant palaeomagnetic directions 36 are normal, 43 reversed and 21 are intermediate; 5% of the dykes are olivine-phyric. The magnetic stratigraphy of the lava pile in this area is partially known from earlier palaeomagnetic studies, and six additional sections measured by field magnetometer and a palaeomagnetic section of 40 flows (20 reversed, 16 normal, and 4 intermediate) are reported here. These sections can be correlated by means of petrologic horizons (silicic tuffs, olivine basalts and porphyritic units) and exhibit stratigraphic thickening towards the centre of the Reydarfjördur dyke swarm. The portion of the basalt pile cut by the dyke swarm can be related both petrologically and palaeomagnetically to the dykes, and the number of exposed dykes is found to be of the same order, but smaller than, the number of lava flows in that comparable portion of the lava pile. This implies that in general the exposed dyke swarm is related to the exposed lava pile which is unlikely to extend much further downdip than the known extension updip. The lava pile in Iceland evolves as large lenticular units formed at eruptive axes, and distributed en échelon along the length of the axial zone with spacings comparable to the thickness of the lithosphere.